5. Fluid Dynamics + Peripheral Circulation Flashcards
Define velocity
The rate of movement of fluid particles along a tube
What is the relationship between velocity and radius for a constant flow?
Velocity is inversely proportional to the radius squared
The greater the cross sectional area the slower the velocity
What is laminar flow?
Where the velocity is greatest in the middle of the vessel and there is a velocity gradient to the edge
What can cause turbulent flow and what does it result in?
Velocity increasing to a point where the flow becomes turbulent
Laminar flow breaks down and resistance is increased greatly
How can you detect turbulent flow?
Creates a noise called bruit
For a constant pressure what is the relationship between velocity and viscosity?
Velocity is inversely proportional to viscosity
The thicker the blood is, the slower it travels
For a constant pressure, what is the relationship between velocity and radius of tube?
As flow is determine by the velocity
Velocity is proportional to radius squared
The wider the tube the faster the blood will travel
Why does increasing radius increase velocity at constant pressure?
The wider the tube the faster the middle layers will move as the velocity gradient is constant
According to poiselles law, what is the relationship between difference in pressure at both ends of a tube and radius at a constant flow and viscosity?
Difference in pressure is inversely proportional to radius to the power of 4
What is the relationship between resistance and viscosity?
Resistance increases as viscosity increases
What is the relationship between resistance and radius?
Resistance decreases with radius to the power of 4
Define flow
Volume of fluid that passes a given point per unit of time
What variables are pressure equal to?
Pressure= flow x resistance
Similar to ohms law with electrical current
What is the relationship between flow and radius for a given pressure?
Flow is proportional to radius to the power of 4
What is the relative pressure size drop over the arteries?
Small
What is the relative pressure drop size over arterioles?
Large
What happens to flow in distensible vessels as pressure is increased and why?
As pressure increases flow increases because:
Increase in pressure causes vessel to stretch
This increases the cross sectional area of the vessel hence flow increases (to the 4th power of the change in radius)
How do veins have capacitance?
A transient increase in pressure will cause more blood to flow into the vessel than out (and vice versa) allowing blood to be “stored” in veins
Why does arterial pressure need to be high?
To drive the cardiac output through the total peripheral resistance
Why do arteries have distensible walls?
So in systole they stretch (more blood flows in than out) hence pressure does not rise too much
As arteries recoil flow continues into arterioles
What factors affect systolic pressure?
How hard the heart pumps
Total peripheral resistance
Stretchiness of arteries
What factors affect diastolic pressure?
Systolic pressure
Total peripheral resistance
What is pulse pressure? (Give a typical value)
Difference between systolic and diastolic pressures
Typically about 40mmHg
How is average pressure calculated?
Diastolic pressure + 1/3 pulse pressure
What properties make arterioles high resistance vessels?
Lumen is narrow
High smooth muscle cell content
What are increases and decreases in vasomotor tone called?
Vasoconstriction
Vasodilatation
Name 3 vasodilator metabolites
H+
K+
Adenosine
How is blood flow matched to rate of metabolism?
Rate of metabolism leads to a proportional amount of metabolites to be produced
Blood flow is then balanced between the rate at which they are produced and how quickly they are washed away
